The present invention relates to flame retardant polycarbonate compositions in the form of blends of polycarbonates and silicone treated fillers such as carbon black and finely divided clays.
Prior to the present invention, as shown by Rich et al, U.S. Pat. No. 4,945,148, flame retardant silicone-polycarbonate block copolymers are provided resulting from the reaction of certain siloxy aromatic imide siloxanes or hydroxy aromatic ester siloxanes which are phosgenated with a dihydric phenol or an aromatic bischloroformate. Lewis describes in U.S. Pat. No. 4,954,549, that triarylsilicon materials, such as triphenolsilanol, can be incorporated into an aromatic polycarbonate to provide transparent, flame retardant, compression moldable thermoplastics. Although various investigations have shown that silicone resins and silicone compounds can reduce the fire hazards of plastics, it has been found that it is necessary to incorporate the silicone into the thermoplastic material utilizing a silicone in the form of a copolymer or nonvolatile compound, since readily available polydiorganosiloxane silicone fluids, such as polydimethylsiloxane fluids, are generally incompatible with thermoplastics and phase separation can occur after simply blending the ingredients.